The preparation of high octane blending components for motor fuels using strong acid alkylation processes (notably where the acid is hydrofluoric acid or sulfuric acid) is well-known. Alkylation is the reaction in which an alkyl group is added to an organic molecule, typically an aromatic or olefin. For production of gasoline blending stocks, the reaction is between an isoparaffin and an olefin. Alkylation processes have been in wide use since World War II when high octane gasolines were needed to satisfy demands from high compression ratio or supercharged aircraft engines. The early alkylation units were built in conjunction with fluid catalytic cracking units to take advantage of the light end by-products of the cracking units: isoparaffins and olefins. Fluidized catalytic cracking units still constitute the major source of feedstocks for gasoline alkylation units. In spite of the mature state of strong acid alkylation technology, existing problems with the hydrofluoric and sulfuric acid technologies continue to be severe: disposal of the used acid, unintentional emission of the acids during use or storage, substantial corrosivity of the acid catalyst systems, and other environmental concerns.
Although a practical alkylation process using solid acid catalysts having little or no corrosive components has long been a goal, commercially viable processes do not exist.
The open literature shows several systems used to alkylate various hydrocarbon feedstocks.
The American Oil Company obtained a series of patents in the mid-1950's on alkylation processes involving C.sub.2 -C.sub.12 (preferably C.sub.2 or C.sub.3) olefins and C.sub.4 -C.sub.8 isoparaffins. The catalysts used were BF.sub.3 -treated solids and the catalyst system (as used in the alkylation process) also contained free BF.sub.3. A summary of those patents is found in the following list:
______________________________________ BF.sub.3 -Treated Catalyst* (with U.S. Pat. No. Inventor free BF.sub.3) ______________________________________ 2,804,491 Kelly et al. SiO.sub.2 stabilized Al.sub.2 O.sub.3 (10%-60% by weight BF.sub.3) 2,824,146 Kelly et al. metal pyrophosphate hydrate 2,824,150 Knight et al. metal sulfate hydrate 2,824,151 Kelly et al. metal stannate hydrate 2,824,152 Knight et al. metal silicate hydrate 2,824,153 Kelly et al. metal orthophosphate hydrate 2,824,154 Knight et al. metal tripolyphosphate hydrate 2,824,155 Knight et al. metal pyroarsenate hydrate 2,824,156 Kelly et al. Co or Mg arsenate hydrate 2,824,157 Knight et al. Co, Al, or Ni borate hydrate 2,824,158 Kelly et al. metal pyroantimonate hydrate salt 2,824,159 Kelly et al. Co or Fe molybdate hydrate 2,824,160 Knight et al. Al, Co, or Ni tungstate hydrate 2,824,161 Knight et al. borotungstic acid hydrate or Ni or Cd borotungstate hydrate 2,824,162 Knight et al. phosphomolybdic acid hydrate 2,945,907 Knight et al. solid gel alumina (5%-100% by weight of Zn or Cu fluoborate, preferably anhydrous) ______________________________________ *may be supported on Al.sub.2 O.sub.3
None of these disclose a process for alkylating olefins and isoparaffins using neat alumina treated with BF.sub.3.
Related catalysts have been used to oligomerize olefins. U.S. Pat. No. 2,748,090 to Watkins suggests the use of a catalyst made up of a Group VIII metal (preferably nickel), a phosphoric acid (preferably containing phosphorus pentoxide), placed on an alumina adsorbent, and pretreated with BF.sub.3. Alkylation of aromatics is suggested.
U.S. Pat. No. 2,976,338 to Thomas suggests a polymerization catalyst comprising a complex of BF.sub.3 or H.sub.3 PO.sub.4 optionally on an adsorbent (such as activated carbon) or a molecular sieve optionally containing potassium acid fluoride.
Certain references suggest the use of alumina-containing catalysts for alkylation of aromatic compounds. U.S. Pat. No. 3,068,301 to Hervert et al. suggests a catalyst for alkylating aromatics using "olefin-acting compounds". The catalyst is a solid, silica-stabilized alumina up to 10% SiO.sub.2, all of which has been modified with up to 100% of weight BF.sub.3. None of the prior references suggest a process nor the material used in the processes disclosed here.
Other BF.sub.3 -treated aluminas are known. For instance, U.S. Pat. No. 3,114,785 to Hervert et al. suggests the use of a BF.sub.3 -modified substantially anhydrous alumina to shift the double bond of 1-butene to produce 2-butene. The preferred alumina is substantially anhydrous gamma-alumina, eta-alumina, or theta-alumina. The various aluminas will adsorb or complex with up to about 19% by weight fluorine depending upon the type of alumina and the temperature of treatment. Hervert et al. does not suggest using these catalysts in alkylation reactions.
In U.S. Pat. No. 4,407,731 to Imai, a high surface area metal oxide such as alumina (particularly gamma-alumina, eta-alumina, theta-alumina, silica, or a silica-alumina) is used as a base or support for BF.sub.3. The BF.sub.3 treated metal oxide is used for generic oligomerization and alkylation reactions. The metal oxide is treated in a complicated fashion prior to being treated with BF.sub.3. The first step entails treating the metal oxide with an acid solution and with a basic aqueous solution. The support is washed with an aqueous decomposable salt such as ammonium nitrate. The support is washed using deionized H.sub.2 O until the wash water shows no alkali or alkaline earth metal cations in the filtrate. The support is dried and calcined. The disclosure suggests generically that BF.sub.3 is then introduced to the treated metal oxide support. The examples show introduction of the BF.sub.3 at elevated temperature, e.g., 300.degree. C. or 350.degree. C.
Similarly, U.S. Pat. No. 4,427,791 to Miale et al. suggests the enhancement of the acid catalytic activity of inorganic oxide materials (such as alumina or gallia) by contacting the material with ammonium fluoride or boron fluoride, contacting the treated inorganic oxide with an aqueous ammonium hydroxide or salt solution, and calcining the resulting material. The inorganic oxides treated in this way are said to exhibit enhanced BrOnsted acidity and, therefore, is said to have improved acid activity towards the catalysis of numerous and several reactions (such as alkylation and isomerization of various hydrocarbon compounds). A specific suggested use for the treated inorganic oxide is as a matrix or support for various zeolite materials ultimately used in acid catalyzed organic compound conversion processes.
U.S. Pat. No. 4,751,341 to Rodewald shows a process for treating a ZSM-5 type zeolite with BF.sub.3 to reduce its pore size, enhance its shape selectivity, and increase its activity towards the reaction of oligomerizing olefins. The patent also suggests using these materials for alkylation of aromatic compounds.
Certain Soviet publications suggest the use of Al.sub.2 O.sub.3 catalysts for alkylation processes. Benzene alkylation using those catalysts (with 3 ppm to 5 ppm water and periodic additions of BF.sub.3) is shown in Yagubov, Kh. M. et al., Azerb. Khim. Zh., 1984, (5) p. 58. Similarly, Kozorezov, Yu and Levitskii, E. A., Zh. Print. Khim. (Leningrad), 1984, 57 (12), p. 2681, show the use of alumina which has been treated at relatively high temperatures and modified with BF.sub.3 at 100.degree. C. There are no indications that BF.sub.3 is maintained in excess. Isobutane alkylation using Al.sub.2 O.sub.3 /BF.sub.3 catalysts is suggested in Neftekhimiya, 1977, 17 (3), p. 396; 1979, 19 (3), P. 385. The olefin is ethylene. There is no indication that BF.sub.3 is maintained in excess during the reaction. The crystalline form of the alumina is not described.
U.S. Pat. No. 4,918,255 to Chou et al. suggests a process for the alkylation of isoparaffins and olefins using a composite described as "comprising a Lewis acid and a large pore zeolite and/or a non-zeolitic inorganic oxide". The process disclosed requires isomerization of the olefin feed to reduce substantially the content of alpha-olefin and further suggests that water addition to the alkylation process improves the operation of the process. The best Research Octane Number (RON) product made using the inorganic oxides (in particular SiO.sub.2) is shown in Table 6 to be 94.0.
U.S. Pat. No. 4,992,616 to Chou et al. deals with the process noted above for alkylation of isoparaffins and olefins using a composite described as "comprising a Lewis acid and a large pore zeolite" but requiring water addition for improvement the operation of the process. The best Research Octane Number (RON) product shown in the examples and made using the disclosed invention is 86.0 (Table 2).
U.S. Pat. No. 4,956,518 to Chow et al. shows an alkylation process using a number of catalysts including one of silica/BF.sub.3. The process also requires the addition of controlled amounts of water. The best RON (Table 3) is shown to be 97.2.
Similarly, PCT published applications WO 90/00533 and 90/00534 (which are based in part on the U.S. patent to Chou et al. noted above) suggest the same process as does Chou et al. WO 90/00534 is specific to a process using boron trifluoride-treated inorganic oxides including "alumina, silica, boria, oxides of phosphorus, titanium oxide, zirconium oxide, chromia, zinc oxide, magnesia, calcium oxide, silica-alumina-zirconia, chromia-alumina, alumina-boria, silica-zirconia, and the various naturally occurring inorganic oxides of various states of purity such as bauxite, clay and diatomaceous earth". Of special note is the statement that the "preferred inorganic oxides are amorphous silicon dioxide and aluminum oxide". The examples show the use of amorphous silica (and BF.sub.3) to produce alkylates having an RON of no greater than 94.
Similarly, U.S. Pat. No. 4,935,577 to Huss, Jr. et al. teaches a process for the catalytic distillation of various hydrocarbons by, e.g., alkylation or oligomerization, using a catalyst "consisting essentially of a Lewis acid promoted inorganic oxide". The inorganic oxide may be selected from the non-zeolitic materials discussed above with regard to the Chou et al. published PCT applications. Additionally, the inorganic oxide may be a large pore crystalline molecular sieve. The best exemplified alkylate appeared to have an RON value of 93 (Table 2).
None of these disclosures show the alkylation of isoparaffins and olefins using crystalline transition aluminas promoted with Lewis acids for the production of high octane gasoline blending components.